Fibrous glass products have been manufactured for many years using precious metal bushings, or glass feeders. Such glass feeders include a foraminous bottom plate, or wall, commonly referred to in the art as a tip plate, which retains a pool of molten glass. Streams of molten glass issue from the openings, or tips, in the bottom bushing wall. By suitable means the streams of glass are then attenuated and collected in the form of fibers. Such glass feeders, or bushings, must be chemically resistant to the action of molten glass and must be dimensionally stable at high operating temperatures. Currently such bushings are manufactured of a precious metal, which term includes elemental precious metals or alloys, such as platinum or platinum and rhodium alloys.
Precious metals are very expensive. If bushings could be formed with smaller amounts of such precious metals and could be formed of cheaper materials, a tremendous economic advantage would be realized. Furthermore, since the precious metal feeders have a limited life, there is a need in the art to provide for bushings which have an improved operating life.
A difficulty which is also encountered in the use of precious metal bushings stems from the fact that oxygen in the air converts exposed precious metal to an oxide which vaporizes and results in the loss of considerable amounts of precious metal during the fiber forming operation. Obviously, there is a need in the art, therefore, to solve this vaporization problem or at least substantially minimize it.
It is also known that after a period of time, precious metal bushings tend to creep or deform in service. Such creep or deformation adversely effects fiber quality. The deformation requires the bushing to be prematurely removed from service, that is, while the corrosive and erosive affects of the glass have not taken their toll on the feeder the deformation has. Thus, there is a need in the art to provide for a bushing having lower creep and deformation.
The present invention now satisfies these needs in the art and solves the problems which resulted from the use of precious metal bushings. A composite bushing is provided which is inexpensively produced and which allows, if desired, for the use of lower amounts of precious metal. These bushings have long life and reduced creep and deformation because they are, in effect, provided with a ceramic reinforcement material. The bushings will be found to have lower vaporization losses and may even provide for lower energy utilization because of their being provided with the ceramic insulating layer.